These historic dry conditions—California is the driest it's been since record-keeping began in the 1890s—are an unfortunate consequence of a naturally occurring weather pattern that's gotten out of hand.

Meteorologists say the drought is thanks largely to a dome of high pressure—or a region of sinking air in the atmosphere—that's been parked over the state for months, with no immediate end in sight.

"It's called a blocking high," said Brian Fuchs, a climatologist at the National Drought Mitigation Center at the University of Nebraska-Lincoln and a co-author of the U.S. Drought Monitor report.

"Not only is it dry under that high pressure, but it is also deflecting all the storm systems that approach [the West Coast]," Fuchs said.

It Should Be Wet

Storms that would normally soak a parched state—and build up California's snowpack—are bouncing off the dome of high pressure, heading into southern Canada, then riding the jet stream south into the U.S. midwest. (Learn more about the high-pressure dome.)

"This is the wet time of year for the West Coast," said Fuchs. "They should be harvesting the water and replenishing their reservoirs."

Instead, the last time downtown Los Angeles saw an appreciable amount of rain was December 19, said the National Weather Service's Jackson. The city has received 23 percent of the precipitation it normally does between July 1 and December 31.

There's little indication that the high-pressure ridge is breaking down, said Fuchs: "Right now, the forecast is warmer and drier conditions through April throughout the western U.S."

The dome of high pressure is the latest in a series of high-pressure ridges that have prompted the drier-than-normal conditions plaguing California for the past two years. (See "Pictures: Drought Parches Much of the U.S.")

High-pressure systems are not unusual for the West Coast, said Fuchs. "[But] when you have an area that starts to dry out and stays warm, it will amplify that high-pressure system."

Jackson added that when a high-pressure dome wobbles to the west, low-pressure systems—regions where air is rising into the atmosphere—squeeze south down the Great Basin in Nevada.

But that leads to additional high-pressure systems that bring ferocious winds called the Santa Anas.